1. Field of the Invention
The present invention relates to a distance measuring system and a projector including the distance measuring system.
2. Description of the Related Art
In these days, projectors are used in many situations which project images displayed on a screen of a personal computer, images produced by video signals, and further images based on image data stored on a memory card on to a screen.
In many cases, projectors are constructed in such a manner that a small, high-intensity light source such as a metal halide lamp or an extra-high pressure mercury lamp is used, light emitted from the light source is passed through a color wheel composed of filters which divides the light into three primary colors of light, the resulting three primary colors of light is then shone on to a liquid crystal display device or a digital micromirror device (DMD) by a group of lens elements referred to as a light source-side optical system, and light that has been passed through or reflected by the display device is projected on to a screen via a group of lens elements referred to as a projection-side optical system which has a zooming function.
In projectors of this type, there occurs a case where a projected image is blurred or a trapezoidal distortion is produced in the projected image depending upon the distance from the projector to the screen, the inclination angle of the screen and the projection angle of image forming light, and in order to eliminate the occurrence of blurred images and/or trapezoidal distortions, the distance between the projector and the screen, the inclination angle of the screen and the projection angle of image forming light need to be measured accurately. To make this happen, a distance measuring system for measuring a distance between the projector and a plurality of points on the screen needs to be provided on the projector.
A distance measuring system for a general projector includes a light source, a receiving element and a receiving lens, wherein light is emitted to an object a distance to which is to be measured or a distance measurement target object, light reflected by the object is made to be concentrated on to the receiving element by the receiving lens, and the receiving element receives the light, from which a distance to the object is calculated by the receiving element. In a distance measuring system like this, much of the light reflected by the distance measurement target object needs to be incident on the receiving element, and a laser beam emitter, the receiving lens and the receiving elements are disposed substantially parallel in different positions. However, a direction in which a laser beam is emitted from the laser beam emitter and a direction in which the receiving elements receives the reflected light differ slightly with respect to their optical axes, and there is caused a position error as to where the reflected light is concentrated depending upon the distance to the distance measurement target object, leading to a problem that the distance measuring range is limited.
Then, to cope with this problem, for example, Japanese Unexamined Patent Publication No. 2002-350543 proposes, as a distance measuring system for a projector, a distance measuring system for measuring a distance to a distance measurement target object by projecting a laser beam emitted from a semiconductor laser device having a linear emitting part to the distance measurement target object via a sending lens system, receiving reflected light reflected by the distance measurement target object by a receiving element via a receiving lens system and processing an electrical signal generated by the receiving element, wherein the semiconductor laser device is provided in such a manner that a longitudinal direction of the linear emitting part of the semiconductor laser device becomes substantially parallel to a plane which connects an optical axis of the sending lens system with an optical axis of the receiving lens system, so as to cover a wide measuring range.
In this invention, since the linear emitting part is made to be included in the plane which connects the optical axis of the sending lens system with the optical axis of the receiving lens system, even though a receiving position error attributed to the deviation of the laser beam emitting direction from the reflected light receiving direction occurs in a near distance measurement, the reflected light only deviates in its longitudinal direction, and therefore, the receiving elements can obtain a sufficient amount of reflected light even in the near distance measurement, whereby the distance measuring system can be provided which has the wide distance measuring range from a far distance to a near distance.